阅读说明：本技术 非对称平面外加速度计 (Asymmetric plane external accelerometer ) 是由 M·汤普森 H·乔哈里-加勒 L·巴尔达萨雷 S·尼灿 K·威廉姆斯 于 2018-08-27 设计创作，主要内容包括：一种微机电(MEMS)加速度计,其基于检测质量块围绕旋转轴线的平面外旋转来感测垂直于MEMS加速度计的MEMS装置平面的线性加速度。对称轴线垂直于旋转轴线。检测质量块包括关于对称轴线对称的对称部分,所述对称部分与关于对称轴线不对称的非对称部分相毗邻。(A micro-electromechanical (MEMS) accelerometer senses linear acceleration perpendicular to a MEMS device plane of the MEMS accelerometer based on out-of-plane rotation of a proof mass about an axis of rotation. The axis of symmetry is perpendicular to the axis of rotation. The proof mass includes a symmetric portion that is symmetric about an axis of symmetry, the symmetric portion being adjacent to an asymmetric portion that is asymmetric about the axis of symmetry.)

1. A micro-electromechanical (MEMS) accelerometer, comprising:

one or more anchors;

a proof mass within a microelectromechanical device layer, comprising a plurality of adjacent sections that collectively rotate about an axis of rotation in response to linear acceleration along a sensing axis, wherein the plurality of adjacent sections of the proof mass comprise:

a symmetry portion symmetrical about an axis of symmetry, wherein the axis of symmetry is perpendicular to the axis of rotation; and

an asymmetric portion that is asymmetric about the axis of symmetry; and

one or more springs within a microelectromechanical device layer coupling the proof mass to the one or more anchors, wherein the one or more springs couple the proof mass to the one or more anchors such that the proof mass rotates about the axis of rotation in response to linear acceleration along the sensing axis.

2. The micro-electromechanical accelerometer of claim 1, wherein the asymmetric portion does not extend through the axis of rotation.

3. The micro-electromechanical accelerometer of claim 1, wherein rotation about the axis of rotation moves the proof mass out of plane.

4. The micro-electromechanical accelerometer of claim 3, wherein the symmetric portion rotates simultaneously above and below the micro-electromechanical device plane in response to the rotation, and the asymmetric portion moves only above or below the micro-electromechanical device plane at any one time.

5. The micro-electromechanical accelerometer of claim 3, wherein the proof mass undergoes rotational motion in the micro-electromechanical device plane in response to a force in the micro-electromechanical device plane.

6. The micro-electromechanical accelerometer of claim 5, further comprising a plurality of bumper stops, wherein at least one of the plurality of bumper stops is positioned adjacent to the asymmetric portion to inhibit rotational motion in a plane of the micro-electromechanical device.

7. The micro-electromechanical accelerometer of claim 6, wherein at least one of the plurality of bumper blocks contacts the asymmetric portion at an angle of at least 15 degrees in response to rotational motion in a plane of the micro-electromechanical device.

8. The micro-electromechanical accelerometer of claim 1, wherein the mass of the asymmetric portion is at least 20% of the mass of the symmetric portion.

9. The micro-electromechanical accelerometer of claim 1, wherein the symmetric portion comprises a plurality of extensions adjacent to at least three sides of the one or more anchors.

10. The micro-electromechanical accelerometer of claim 9, wherein the asymmetric portion is not adjacent to any side of the one or more anchors.

11. The micro-electromechanical accelerometer of claim 10, wherein the plurality of extensions are substantially rectangular in shape.

12. The micro-electromechanical accelerometer of claim 10, wherein the asymmetric portion is substantially rectangular in shape.

13. The micro-electromechanical accelerometer of claim 1, further comprising:

one or more second anchors;

a second proof mass within the microelectromechanical device layer, the second proof mass comprising a plurality of second adjacent portions that collectively rotate about a second axis of rotation in response to linear acceleration along a sensing axis, wherein the plurality of second adjacent portions of the second proof mass comprise:

a second symmetry section symmetrical about a second symmetry axis, wherein the second symmetry axis is perpendicular to the second rotation axis; and

a second asymmetric portion asymmetric about the second axis of symmetry; and

one or more second springs within a microelectromechanical device layer coupling the second proof mass to the one or more second anchors, wherein the one or more second springs couple the second proof mass to the one or more second anchors such that the second proof mass rotates about the second axis of rotation in response to linear acceleration along the sensing axis.

14. The micro-electromechanical accelerometer of claim 13, wherein the second proof mass and the proof mass have substantially the same shape.

15. The micro-electromechanical accelerometer of claim 13, wherein rotation of the second proof mass in response to the linear acceleration and rotation of the proof mass in response to the linear acceleration are in anti-phase.

16. The micro-electromechanical accelerometer of claim 15, wherein at least a portion of the first asymmetric portion is positioned adjacent to at least a portion of the second asymmetric portion and at least a portion of the second asymmetric portion is positioned adjacent to at least a portion of the first symmetric portion.

17. The micro-electromechanical accelerometer of claim 13, wherein the first axis of rotation and the second axis of rotation comprise the same axis.

18. The micro-electromechanical accelerometer of claim 13, wherein the first and second axes of rotation are parallel to each other.

19. A micro-electromechanical (MEMS) accelerometer, comprising:

one or more anchors, wherein the axis of symmetry and the axis of rotation intersect within an area defined by the one or more anchors;

a proof mass within a microelectromechanical device layer, wherein the proof mass collectively rotates about the axis of rotation in response to linear acceleration along a sensing axis, and a first portion of the proof mass is symmetric about the axis of symmetry and a second portion of the proof mass is asymmetric about the proof mass; and

one or more springs within a microelectromechanical device layer coupling the proof mass to the one or more anchors, wherein the one or more springs couple the proof mass to the one or more anchors such that the proof mass rotates about the axis of rotation in response to linear acceleration along the sensing axis.

20. A micro-electromechanical (MEMS) accelerometer, comprising:

a first proof mass suspended within a microelectromechanical device layer and including a plurality of first adjacent portions that collectively rotate about an axis of rotation in response to linear acceleration along a sensing axis, wherein the plurality of first adjacent portions of the first proof mass comprise:

a first symmetrical portion symmetrical about a first axis of symmetry, wherein the first axis of symmetry is perpendicular to the axis of rotation; and

a first asymmetric portion asymmetric about the first axis of symmetry; and

a second proof mass suspended within the microelectromechanical device layer and including a plurality of second adjacent portions that collectively rotate about the axis of rotation in antiphase with respect to the first proof mass in response to linear acceleration along the sensing axis, wherein the plurality of second adjacent portions of the second proof mass include:

a second symmetry section symmetrical about a second symmetry axis, wherein the second symmetry axis is perpendicular to the rotation axis and parallel to the first symmetry axis; and

a second asymmetric portion asymmetric about the second axis of symmetry.

Background

Many items, such as smartphones, smartwatches, tablets, automobiles, aerial drones, appliances, aircraft, sports aids, and game controllers, may utilize motion sensors during their operation. In many applications, various types of motion sensors, such as accelerometers and gyroscopes, may be analyzed separately or together to determine a wide variety of information for a particular application. For example, gyroscopes and accelerometers may be used in gaming applications (e.g., smart phones or game controllers) to capture complex motions of a user, drones and other aerial vehicles may determine orientation (e.g., roll, pitch, and yaw) based on gyroscope measurements, and vehicles may utilize measurements to determine direction (e.g., for dead reckoning) and safety (e.g., to identify slip or roll conditions).

Motion sensors, such as accelerometers and gyroscopes, may be fabricated as micro-electromechanical (MEMS) sensors fabricated using semiconductor fabrication techniques. MEMS sensors may include a movable proof mass (proof mass) that may respond to forces such as linear acceleration (e.g., for MEMS accelerometers), angular velocity (e.g., for MEMS gyroscopes), magnetic fields, and many other forces. The effect of these forces on the movable proof mass can be measured based on the motion of the proof mass in response to these forces. In some implementations, the motion of the proof mass is converted to an electrical signal by the capacitive sensing electrodes.

In a typical MEMS sensor, the proof mass may be positioned in close proximity to a plurality of fixed surfaces. The fixed electrodes, anchors, external frame may be positioned within the same device layer as the proof mass and adjacent to the proof mass. In the presence of undesirable external forces (e.g., impacts), the proof mass may be caused to contact a fixed surface, causing wear or even catastrophic damage. Even small undesirable external forces that do not cause the proof mass to contact the fixed surface may affect the motion of the proof mass and thus the accuracy of the results of the measured parameters.

Disclosure of Invention

In an exemplary embodiment of the present disclosure, a microelectromechanical (MEMS) accelerometer can include one or more anchors and a proof mass within a MEMS device layer, the proof mass including a plurality of adjacent portions that collectively rotate about an axis of rotation in response to linear acceleration along a sensing axis, wherein the plurality of adjacent portions of the proof mass include: a symmetry portion symmetrical about an axis of symmetry, wherein the axis of symmetry is perpendicular to the axis of rotation; and an asymmetric portion that is asymmetric about an axis of symmetry. In some embodiments, one or more springs located within the MEMS device layer couple the proof mass to the one or more anchors, wherein the one or more springs couple the proof mass to the one or more anchors such that the proof mass rotates about the axis of rotation in response to linear acceleration along the sensing axis.

In an exemplary embodiment of the present disclosure, a micro-electromechanical (MEMS) accelerometer may include: one or more anchors, wherein the axis of symmetry and the axis of rotation intersect within an area defined by the one or more anchors; and a proof mass located within the MEMS device layer, wherein the proof mass collectively rotates about the axis of rotation in response to linear acceleration along a sensing axis, and wherein a first portion of the proof mass is symmetric about the axis of symmetry and a second portion of the proof mass is asymmetric about the proof mass. In some embodiments, one or more springs located within the MEMS device layer couple the proof mass to the one or more anchors, wherein the one or more springs couple the proof mass to the one or more anchors such that the proof mass rotates about the axis of rotation in response to linear acceleration along the sensing axis.

In an embodiment of the present disclosure, a microelectromechanical (MEMS) accelerometer can include a first proof mass suspended within a MEMS device layer and including a plurality of first adjacent portions that collectively rotate about an axis of rotation in response to linear acceleration along a sensing axis, wherein the plurality of first adjacent portions of the first proof mass include: a first symmetrical portion symmetrical about a first axis of symmetry, wherein the first axis of symmetry is perpendicular to the axis of rotation; and a first asymmetric portion that is asymmetric about a first axis of symmetry. In some embodiments, the MEMS accelerometer may further comprise a second proof mass suspended within the MEMS device layer and comprising a plurality of second adjacent portions that collectively rotate about the rotation axis in antiphase with respect to the first proof mass in response to linear acceleration along the sensing axis, wherein the plurality of second adjacent portions of the second proof mass comprise: a second symmetry section symmetrical about a second symmetry axis, wherein the second symmetry axis is perpendicular to the rotation axis and parallel to the first symmetry axis; and a second asymmetric portion that is asymmetric about a second axis of symmetry.

Drawings

The above and other features of the present disclosure, its nature and various advantages will be more apparent from the following detailed description when considered in conjunction with the accompanying drawings in which:

FIG. 1 shows an illustrative motion sensing system according to an embodiment of the present disclosure;

figure 2A shows an illustrative symmetric proof mass according to some embodiments of the present disclosure;

figure 2B shows an illustrative asymmetric proof mass according to some embodiments of the present disclosure;

FIG. 3 shows an illustrative out-of-plane sensing accelerometer, according to some embodiments of the present disclosure;

figure 4A illustrates movement of the asymmetric proof mass of figure 3 relative to a bump stop in response to linear acceleration in a single translational plane, in accordance with some embodiments of the present disclosure;

FIG. 4B illustrates movement of the asymmetric proof mass of FIG. 3 relative to a bumper stop in response to linear acceleration in a multi-directional plane according to some embodiments of the present disclosure; and

figure 5 shows an illustrative MEMS device plane of an out-of-plane sensing accelerometer, according to some embodiments of the present disclosure.

Detailed Description

The accelerometer is designed and manufactured as a micro-electromechanical (MEMS) accelerometer. The MEMS layer is formed using semiconductor processing techniques to include the mechanical components of the sensor and electrical connections to other components of the MEMS accelerometer, such as CMOS circuitry located within the sensor die (e.g., CMOS layer, also serving as a substrate or cap layer) or external to the sensor die. The MEMS layer is hermetically sealed within other semiconductor layers, such as underlying substrate and cap layers.

The MEMS layer includes a suspended spring-mass system, wherein one or more proof masses are suspended within the MEMS layer by springs. The motion of the proof mass is limited by springs and, in some embodiments, other components such as a mass and levers. These springs and additional components collectively facilitate movement of a proof mass along one or more axes, which is used to sense linear acceleration. A sense electrode is adjacent each proof mass in the direction of the sensed linear acceleration, forming a capacitor that varies based on the distance between the proof mass and the sense electrode.

The MEMS accelerometer may be a z-axis accelerometer that senses z-axis linear acceleration based on motion of the proof mass out of plane. The z-axis linear acceleration rotates the proof masses about the axis of rotation, a portion of each proof mass moves out of plane toward some of the sense electrodes (e.g., increasing capacitance), and a portion of each proof mass moves away from some of the sense electrodes (e.g., increasing capacitance). Each proof mass may include a symmetric portion and an asymmetric portion. The symmetry portion may be symmetrical about a symmetry axis, which may intersect the rotation axis at the anchoring point. In response to large undesirable forces (e.g., forces other than linear acceleration along the z-axis), the asymmetric portion of the proof mass may result in rotational coupling of the forces that causes the proof mass to rotate about the anchor point.

The buffer stops may extend from a fixed portion of the MEMS layer adjacent to the proof mass to prevent damage due to excessive travel of the proof mass in response to large unwanted forces (e.g., impacts). The buffer stop may be dimensioned and placed at a position relative to the proof mass in such a way that it will contact the proof mass when the rotation of the proof mass exceeds a rotation threshold, in degrees, for example 5-35 degrees (e.g. 15 degrees). The bumper stops may be sized and positioned such that rotational movement causes more bumper stops that the proof mass contacts than would be the case with translational movement, resulting in a greater distribution of impact forces from the proof mass to the bumper stops and reducing the likelihood of damage due to large unwanted forces.

During normal operation, the MEMS accelerometer will experience other undesirable forces in addition to the force to be measured, but these other undesirable forces will not be large enough to contact the bump stops. However, such forces may cause measurement errors due to vibration correction error (VRE), a condition that causes the sensing electrodes to output a non-zero bias signal. Because it is difficult to measure the vibration correction error during operation, it may be difficult to compensate for the non-zero bias signal during operation. At least some of these unwanted forces may couple to the forces generated by the asymmetric proof mass in a manner that may result in a reduction in VRE.

The MEMS moveable component (e.g., proof mass) may be positioned in close proximity to other moveable components and fixed portions that lie within the plane of the MEMS device. This close proximity may result in physical contact of the components at rest due to manufacturing tolerances, wear over time, and other conditions. Stiction may refer to the condition where the surface adhesion force exceeds the mechanical restoring force of one or more MEMS movable components. The asymmetric proof mass portion generates a torque with respect to an applied linear force (e.g., impact), which causes rotation of the MEMS moveable component, thereby forming a tilted contact between the surface of the proof mass and the other MEMS components, thereby reducing surface adhesion forces that cause stiction.

Fig. 1 illustrates an exemplary motion sensing system 10 according to some embodiments of the present disclosure. Although specific components are depicted in fig. 1, it should be understood that other suitable combinations of sensors, processing components, memory, and other circuitry may be used depending on the needs of different applications and systems. In embodiments as described herein, the motion sensing system may include at least a MEMS accelerometer 12 (e.g., an out-of-plane sensing accelerometer) and supporting circuitry, such as processing circuitry 14 and memory 16. In some embodiments, one or more additional sensors 18 (e.g., additional MEMS gyroscopes, MEMS accelerometers, MEMS microphones, MEMS pressure sensors, and compasses) may be included within the motion sensing system 10 to provide an integrated motion processing unit ("MPU") (e.g., including 3-axis MEMS gyroscope sensing, 3-axis MEMS accelerometer sensing, microphones, pressure sensors, and compasses).

Processing circuitry 14 may include one or more components that provide the necessary processing based on the requirements of motion sensing system 10. In some embodiments, the processing circuitry 14 may include hardware control logic that may be integrated within the chip of the sensor (e.g., on a substrate or lid of the MEMS accelerometer 12 or other sensor 18, or on a portion of the chip adjacent to the MEMS accelerometer 12 or other sensor 18) to control operation of the MEMS accelerometer 12 or other sensor 18 and to perform various aspects of the processing of the MEMS accelerometer 12 or other sensor 18. In some embodiments, the MEMS accelerometer 12 or other sensor 18 may include one or more registers that allow various aspects of the operation of the hardware control logic to be modified (e.g., by modifying the values of the registers). In some embodiments, processing circuitry 14 may also include a processor, such as a microprocessor, that executes software instructions, for example, stored in memory 16. The microprocessor may control the operation of the MEMS accelerometer 12 by interacting with hardware control logic and processing the measurement signals received from the MEMS accelerometer 12. The microprocessor may interact with other sensors in a similar manner.

While IN some embodiments (not depicted IN FIG. 1), MEMS accelerometer 12 or other sensors 18 may be IN direct communication with external circuitry (e.g., via a serial bus or directly connected to sensor outputs and control inputs), IN one embodiment, processing circuitry 14 may process data received from MEMS accelerometer 12 and other sensors 18 and communicate with external components via a communication interface 20 (e.g., SPI or I2C bus, or IN automotive applications, a Controller Area Network (CAN) bus or a local Internet (L IN) bus). processing circuitry 14 may convert signals received from MEMS accelerometer 12 and other sensors 18 into appropriate units of measurement (e.g., based on settings provided by other computing units communicating over communication bus 20) and perform more complex processing to determine measurements such as orientation or Euler angles, and IN some embodiments, determine whether particular activities (e.g., walking, running, braking, skidding, rolling, etc.) are occurring based on the sensor data.

In certain embodiments, certain types of information may be determined based on data from the plurality of MEMS accelerometers 12 and other sensors 18 in a process that may be referred to as sensor fusion. By combining information from various sensors, information useful in various applications can be accurately determined, such as image stabilization, navigation systems, automotive control and security, dead reckoning, remote control and gaming devices, activity sensors, three-dimensional cameras, industrial automation, and many other applications.

An exemplary MEMS accelerometer (e.g., MEMS accelerometer 12) may include one or more movable proof masses configured in a manner that allows the MEMS accelerometer (e.g., MEMS accelerometer or MEMS gyroscope) to measure a desired force (e.g., linear acceleration along an axis). In some embodiments, the one or more movable proof masses may be suspended from anchor points, which may refer to any fixed portion of the MEMS sensor, such as anchors extending from a layer (e.g., CMOS layer) parallel to the MEMS layer of the device, a frame of the MEMS layer of the device, or any other suitable portion of the MEMS device that is fixed relative to the movable proof mass. The proof masses may be arranged such that they move in a desired direction in response to linear acceleration. In an exemplary embodiment, out-of-plane motion of the proof mass relative to a fixed surface (e.g., a fixed sensing electrode located below relative to a movable proof mass on a substrate) in response to measured linear acceleration is measured and scaled to determine acceleration along a sensing axis.

Fig. 2A depicts an exemplary proof mass 202 of a MEMS accelerometer suitable for in-plane applied velocity sensing, according to some embodiments of the present disclosure. The proof mass 202 is formed within the MEMS device layer and includes two parallel MEMS device planes on opposite sides of the MEMS device layer, forming parallel x-y planes. Although not depicted in fig. 2A, the substrate layer may be positioned parallel to one of the planes of the MEMS device, while the cap layer may be positioned parallel to another of the planes of the MEMS device.

In the context of the present disclosure, the MEMS device plane located closest to the parallel substrate layers may be referred to as the bottom MEMS device plane, while the MEMS device plane located furthest from the parallel substrate layers may be referred to as the top MEMS device plane, although it should be understood that "top" and "bottom" are any terms describing relative positions and may be interchanged or otherwise modified as appropriate. The views of FIGS. 2A-2B may depict top views of the top MEMS device layers. Although not depicted in FIGS. 2A-2B, the substrate layer is positioned parallel to the bottom MEMS device plane. The sense electrodes are positioned on the substrate layer below portions of the proof mass 202, forming one or more capacitors with the proof mass 202 that change capacitance based on motion of the proof mass 202 relative to the sense electrodes along the z-axis.

Anchors 208 can be positioned in the MEMS device plane and coupled to the substrate layer and/or the cover layer such that anchors 208 do not move relative to the substrate in response to forces experienced during normal operating conditions of the MEMS accelerometer. Springs 212 and 214 couple proof mass 202 to anchor 208 such that proof mass 202 is suspended from anchor 208 in the MEMS device plane. In one embodiment, the springs 212 and 214 may be torsionally compliant about the x-axis to allow the proof mass 202 to rotate about the axis of rotation 218 in response to linear acceleration along the z-axis.

In some embodiments, the proof mass 202 may include two symmetric portions 204 and 206 about an axis of symmetry 210, and may be asymmetric about an axis of rotation 218. The proof mass 202 may have a center of mass 216 located along the axis of symmetry 210 but offset from the axis of rotation 218 in the positive y-direction. The location of the center of mass 216 may facilitate movement of the proof mass 202 in response to linear acceleration along the z-axis. Linear acceleration in the positive z-direction may cause the center of mass 216 of the proof mass 202 to move in the negative z-direction about the axis of rotation 218. An upper portion 205 of the proof mass 202 (e.g., the portion positioned in the positive y-direction of the rotation axis 218) may move toward the substrate and any sense electrodes located below the upper portion 205, thereby increasing the capacitance associated with those sense electrodes. The lower portion 207 of the proof mass 202 (e.g., the portion located in the negative y-direction of the axis of rotation 218) may move away from the substrate and any sense electrodes located below the lower portion 207, thereby reducing the capacitance associated with those sense electrodes. Linear acceleration in the positive z direction may be determined based on one or both of these changes in capacitance.

Linear acceleration in the negative z-direction can cause the center of mass 216 of the proof mass 202 to move in the positive z-direction about the axis of rotation 218. The upper portion 205 can be moved away from the substrate and any sensing electrodes located below the upper portion 205, thereby reducing the capacitance associated with those sensing electrodes. Lower portion 207 may be moved toward the substrate and any sensing electrodes located below lower portion 207, thereby increasing the capacitance associated with those sensing electrodes. Linear acceleration in the negative z-direction may be determined based on one or both of these changes in capacitance.

Figure 2B depicts an example asymmetric proof mass 222 of a MEMS accelerometer suitable for in-plane applied velocity sensing, according to some embodiments of the present disclosure. The asymmetric proof mass 222 is formed within the MEMS device layer and includes two parallel MEMS device planes on opposite sides of the MEMS device layer, forming parallel x-y planes. Although not depicted in fig. 2B, the substrate layer may be positioned parallel to one of the planes of the MEMS device, while the cap layer may be positioned parallel to another of the planes of the MEMS device.

The view of FIG. 2B may depict a top view of the top MEMS device layer. Although not depicted in FIG. 2B, the substrate layer is positioned parallel to the bottom MEMS device plane. The sense electrodes are located on substrate layers below portions of the asymmetric proof mass 222, forming one or more capacitors with the asymmetric proof mass 222 that change capacitance based on motion of the asymmetric proof mass 222 relative to the sense electrodes along the z-axis.

The anchor 228 may be located in the plane of the MEMS device and coupled to the substrate layer and/or the cover layer such that the anchor 228 does not move relative to the substrate in response to forces experienced during normal operating conditions of the MEMS accelerometer. Springs 232 and 234 couple the asymmetric proof mass 222 to the anchor 228 such that the asymmetric proof mass 222 is suspended from the anchor 228 within the MEMS device plane. In one embodiment, the springs 232 and 234 may be torsionally compliant about the x-axis to allow the asymmetric proof mass 222 to rotate about the rotation axis 240 in response to linear acceleration along the z-axis.

In some embodiments, the asymmetric proof mass 222 may include two symmetric portions 224 and 226 about an axis of symmetry 242. The asymmetric proof mass 222 may also include an adjacent asymmetrically extending portion 244 extending from one of the symmetric portions 224 and 226 (in some embodiments, the symmetric portions 224 and 226 may be collectively referred to as the symmetric portion of the asymmetric proof mass 222). The asymmetric proof mass 222 (e.g., symmetric portions 224 and 226 and asymmetric extension 244) may have a center of mass 236 that is offset from the axis of symmetry 242 in the positive x-direction based on the additional mass of the asymmetric extension 244. The center of mass 236 of the asymmetric proof mass 222 is offset from the axis of rotation 218 in the positive y-direction based on the additional mass of the symmetric portions 224 and 226 and the additional mass of the asymmetric extension 244.

The position of the center of mass 236 can facilitate movement of the asymmetric proof mass 222 in response to linear acceleration along the z-axis. External forces along other axes may couple to the desired out-of-plane motion of the asymmetric portion 244, thereby greatly reducing undesirable phenomena such as VRE. Linear acceleration in the positive z-direction can cause the center of mass 236 of the asymmetric proof mass 222 to move in the negative z-direction about the axis of rotation 238. The upper portion 225 (e.g., the portion positioned in the positive y-direction of the rotational axis 238) of the asymmetric proof mass 222 may move toward the substrate and any sense electrodes located below the upper portion 225, thereby increasing the capacitance associated with these sense electrodes. The lower portion 227 of the asymmetric proof mass 222 (e.g., the portion positioned in the negative y-direction of the rotation axis 218) may be moved away from the substrate and any sense electrodes located below the lower portion 227, thereby reducing the capacitance associated with those sense electrodes. Linear acceleration in the positive z direction may be determined based on one or both of these changes in capacitance.

Linear acceleration in the negative z-direction can cause the center of mass 236 of the asymmetric proof mass 222 to move in the positive z-direction about the axis of rotation 238. The upper portion 225 can be moved away from the substrate and the sensing electrodes located below the upper portion 225, thereby reducing the capacitance associated with those sensing electrodes. Lower portion 227 may be moved toward the substrate and any sense electrodes located below lower portion 227, thereby increasing the capacitance associated with those sense electrodes. Linear acceleration in the negative z-direction may be determined based on one or both of these changes in capacitance.

Acceleration in a linear plane along x or y not only applies a linear force to the proof mass 222, but also applies a torque to the proof mass 222 because the center of mass is offset from the center of rotation at the center of anchoring where the axis of rotation 238 intersects the axis of symmetry 242. This causes the proof mass to not only translate but also rotate in-plane. It is advantageous to translate and rotate the proof mass due to these linear inputs. For large in-plane impacts, the rotational and linear motion of the proof mass will share the energy of excitation, eliminating the concentration of energy that could lead to damage and failure. For smaller impacts, translation and rotation may help reduce the contact area associated with adhesion and prevent stiction. There will be one input direction with the center of rotation and centroid 236 aligned, but the input direction can be optimized so that it is not aligned with the direction of least stiffness typically designed along the x, y, or z axis.

Fig. 3 shows an illustrative out-of-plane sensing accelerometer, according to some embodiments of the present disclosure. Those of ordinary skill in the art will appreciate, in light of this disclosure, that FIG. 3 may be modified in various ways. The components of FIG. 3 are formed within a MEMS device layer and include two parallel MEMS device planes on opposite sides of the MEMS device layer, forming parallel x-y planes. Although not depicted in fig. 3, the substrate layer may be positioned parallel to one of the planes of the MEMS device, while the cap layer may be positioned parallel to another of the planes of the MEMS device.

In some embodiments, the accelerometer of figure 3 may include a first sensor portion 370 and a second sensor portion 380, each including similar or identical components. The first and second sensor portions are oriented such that a center of mass associated with the proof mass 302 (i.e., the proof mass of the first sensor portion 370) and the proof mass 318 (i.e., the proof mass of the first sensor portion 370) cause anti-phase motion about the x-axis in response to linear acceleration along the z-axis. The first 370 and second 380 sensor portions are surrounded by a MEMS stationary portion 390, which is depicted in fig. 3 with diagonal lines.

In an embodiment, the first sensor portion 370 includes an anchor 310, which may be coupled to the paddle masses 306 and 314 by connecting rods 308 and 312. Paddle masses 306 and 314 may be coupled to proof mass 302 by springs 304 and 316. The connecting rods 308 and 312 may be substantially rigid, but may facilitate rotational movement of the paddle masses 306 and 314 and the proof mass 302 about the rotational axis 366. The springs 304 and 316 may be substantially rigid along the x-axis, may allow limited motion along the y-axis, and may have significant torsional compliance to allow the proof mass 302 to rotate about the rotation axis 366. The axis of symmetry 360 may be perpendicular to the axis of rotation 366 and may intersect the axis of rotation at a center point of the anchor 310. Proof mass 302 may include a symmetric proof mass portion 372 and an asymmetric proof mass portion 374. The symmetric proof mass portion 372 may be symmetric about the axis of symmetry 360. An asymmetric proof mass portion 374 may extend from the symmetric proof mass portion 372 such that the proof mass 302 as a whole is asymmetric and has no axis of symmetry. The center of mass 392 of the proof mass 302 may be offset from the axis of symmetry 360 in the positive x-direction and may be offset from the axis of rotation 366 in the positive y-direction.

In some embodiments, a plurality of buffer stops may extend from the MEMS fixed portion 390 toward the movable member (e.g., proof mass 302). The buffer stop may provide a surface that is contacted in the event of excessive travel or impact, such as of the proof mass. In an exemplary embodiment, six substantially rectangular buffer stops 334, 336, 338, 340, and 342 may be positioned at various locations adjacent the proof mass 302, although it will be appreciated that additional or fewer buffer stops of suitable shape and size may be implemented in different embodiments in accordance with the present disclosure.

In an exemplary embodiment, a buffer stop 334 may be positioned adjacent the lower left portion of the symmetric proof mass portion 372 to inhibit translational movement of the proof mass 302 in the negative y-direction. The buffer stops 334 may also be positioned such that rotation (or combined translational and rotational motion) of the proof mass 302 about the z-axis may cause the lower left portion of the symmetric proof mass portion 372 to contact the stops 334 at an angle. In an exemplary embodiment, the size and position of the buffer stop 334 relative to the proof mass may be designed such that the proof mass 302 may contact the buffer stop 334 in response to rotation of the proof mass beyond a rotation threshold in the range of 5-35 degrees (e.g., 15 degrees in an exemplary embodiment). In an embodiment, the buffer stops 336, 338, 340, and 342 may be positioned relative to the proof mass in a similar manner to limit translational movement of the proof mass 302 in a direction and further inhibit rotation of the proof mass 302 beyond a rotation threshold. Although each bump stop may be designed and positioned to have a different threshold of rotation, in an exemplary embodiment, each bump stop may have a similar or identical threshold of rotation.

In an embodiment, first sensor portion 380 includes an anchor 326, which may be coupled to paddle masses 322 and 330 by connecting rods 324 and 328. Paddle masses 322 and 330 may be coupled to proof mass 318 by springs 320 and 332. The connecting rods 324 and 328 may be substantially rigid, but may facilitate rotational movement of the paddle masses 322 and 330 and the proof mass 318 about the rotational axis 366. The springs 320 and 332 may be substantially rigid along the x-axis, may allow limited motion along the y-axis, and may have significant torsional compliance to allow the proof mass 318 to rotate about the rotation axis 366. Although in the exemplary embodiment of fig. 3, the first and second sensor portions 370 and 380 have a common axis of rotation 366, in other embodiments, each of the sensor portions 370 and 380 may have a unique axis of rotation (e.g., parallel or at an angle). The axis of symmetry 364 can be perpendicular to the axis of rotation 366 and can intersect the axis of rotation at a center point of the anchor 326. Proof mass 318 may include symmetric proof mass portions 382 and asymmetric proof mass portions 384. The symmetric proof mass portion 382 may be symmetric about the axis of symmetry 364. An asymmetric proof mass section 384 may extend from the symmetric proof mass section 382 such that the proof mass 318 is asymmetric as a whole and has no axis of symmetry. The center of mass 394 of the proof mass 318 may be offset from the axis of symmetry 364 in the negative x-direction and may be offset from the axis of rotation 366 in the negative y-direction.

In some embodiments, a plurality of buffer stops may extend from the MEMS fixed portion 390 toward the proof mass 318. The buffer stop may provide a surface that is contacted in the event of excessive travel or impact, such as by the proof mass. In an exemplary embodiment, six substantially rectangular buffer stops 344, 346, 348, 350 and 352 may be positioned at various locations adjacent to the proof mass 318, although it will be appreciated that additional or fewer buffer stops of suitable shape and size may be implemented in different embodiments in accordance with the present disclosure.

In an exemplary embodiment, the buffer stop 344 may be positioned adjacent the upper right portion of the symmetric proof mass portion 382 to inhibit translational movement of the proof mass 318 in the positive y-direction. The buffer stops 344 may also be positioned such that rotation (or combined translational and rotational motion) of the proof mass 318 about the z-axis may cause the upper right portion of the symmetric proof mass portion 382 to contact the buffer stops 344 at an angle. In an exemplary embodiment, the size and position of the buffer stops 344 relative to the proof mass may be designed such that the proof mass 318 may contact the buffer stops 344 in response to rotation of the proof mass beyond a rotation threshold in the range of 5-35 degrees (e.g., 15 degrees in an exemplary embodiment). In an embodiment, the buffer stops 346, 348, 350, and 352 may be positioned relative to the proof mass in a similar manner to limit translational movement of the proof mass 318 in a direction and further inhibit rotation of the proof mass 318 beyond a rotation threshold. Although each bump stop may be designed and positioned to have a different threshold of rotation, in an exemplary embodiment, each bump stop may have a similar or identical threshold of rotation.

Linear acceleration in the positive z direction can cause the center of mass 392 of the proof mass 302 to move in the negative z direction about the axis of rotation 366, and can cause the center of mass 394 of the proof mass 318 to move in the negative z direction about the axis of rotation 366. The asymmetric proof mass portion 374 and the portions of the symmetric proof mass portion 372 located in the positive y-direction from the axis of rotation 366 can move toward the substrate and any sense electrodes located below these portions of the proof mass 302. Other portions of the proof mass 302 may move away from the substrate and any sensing electrodes located below these other portions of the proof mass 302. The asymmetric proof mass section 384 and the portions of the symmetric proof mass section 382 that are positioned in the negative y-direction from the axis of rotation 366 are movable towards the substrate and any sensing electrodes located below these portions of the proof mass 318. Other portions of the proof mass 318 may move away from the substrate and any sensing electrodes located below these other portions of the proof mass 318.

Linear acceleration in the negative z-direction can cause the center of mass 392 of the proof mass 302 to move in the positive z-direction about the axis of rotation 366, and can cause the center of mass 394 of the proof mass 318 to move in the positive z-direction about the axis of rotation 366. The asymmetric proof mass portion 374 and the portions of the symmetric proof mass portion 372 located in the positive y-direction from the axis of rotation 366 can move away from the substrate and any sense electrodes located below these portions of the proof mass 302. Other portions of the proof mass 302 may move toward the substrate and any sensing electrodes located below these other portions of the proof mass 302. The asymmetric proof mass portion 384 and the portions of the symmetric proof mass portion 382 located in the negative y-direction from the rotation axis 366 can move away from the substrate and any sensing electrodes located below these portions of the proof mass 318. Other portions of the proof mass 318 may move toward the substrate and any sensing electrodes located below these other portions of the proof mass 318.

In an exemplary embodiment, a paddle mass may be coupled to each proof mass to facilitate sensor deflection stability. The sensing electrodes may be located on the substrate plane below the proof mass to perform differential capacitive sensing based on rotation of the proof masses 302 and 318 about the rotation axis 366. A torsion spring coupled between each proof mass and the anchor and the paddle mass may suspend the paddle mass and the proof mass and may allow the proof mass to rotate about the axis of rotation. In this manner, rotation of the proof mass 302 about the rotation axis 366 increases or decreases the capacitance associated with portions of the proof mass based on the position and rotational orientation of the sense electrodes. Based on the position and rotational orientation of the sense electrodes, rotation of the proof mass 318 about the rotational axis 366 increases or decreases the capacitance associated with portions of the proof mass.

Figure 4A illustrates movement of the asymmetric proof mass (e.g., proof mass 302) of figure 3 relative to a bumper stop in response to linear acceleration in a single plane, according to some embodiments of the present disclosure. For ease of illustration, other components (e.g., paddle mass, torsion spring, anchor, second sensor portion, etc.) are omitted from fig. 4A. It will be understood that in some embodiments, the buffer stops depicted in figure 4A may have different shapes, may be positioned at different locations relative to the proof mass 302, and may be positioned at different distances relative to the proof mass 302. It will be appreciated that in some embodiments, one or more additional buffer stops may be added, as well as one or more of the described buffer stops may be removed.

Figure 4A shows the motion of the proof mass 302 during an undesired linear acceleration due to an impact in the positive y-direction. In the exemplary embodiment of FIG. 4A, the impact is idealized so that it is not forced in the x-direction. Due to the linear acceleration in the positive y-direction only, the proof mass 302 translates in the positive y-direction and rotates about the z-axis to contact the bumper block 340. The upper x-z planar surface of the proof mass 302 contacts the lower x-z planar surface of the buffer stop 340 at an angle.

Figure 4B shows the motion of the proof mass 302 during an undesired linear acceleration due to an impact in the positive x-direction. The asymmetric shape of the proof mass causes the proof mass 302 to move rotationally in response to linear acceleration in the x-direction. Even when the force in one of the x-direction or y-direction is significantly greater (e.g., an order of magnitude greater) than the other forces, the asymmetric shape of the proof mass may result in rotational coupling of the forces and rotation of the proof mass 302 about the anchor 310.

In an embodiment, counterclockwise rotation about anchor 310 may cause proof mass 302 to contact each of buffer stops 334, 336, 340, and 342. The lower left x-z surface of the proof mass 302 may contact the buffer stop 334, the upper left y-z surface may contact the buffer stop 336, the upper right x-z surface of the proof mass 302 may contact the buffer stop 340, and the upper right y-z surface of the proof mass 302 may contact the buffer stop 342. In the exemplary embodiment of FIG. 4B, instead of a single surface contacting two bumper stops, four surfaces of the proof mass 302 contact four bumper stops. This improves the impact force distribution from the proof mass 302 to the additional bumper. The shape of the asymmetric proof mass 302 supports this distribution of forces by causing rotation of the proof mass under most impact conditions.

An angled impact through both the center of rotation of the spring and the center of mass of the proof mass will cause the proof mass to translate without rotation. This angled impact will be in a direction different from the direction of minimum stiffness of the spring. Thus, during the time that the proof mass contacts the bumper, the spring restoring force increases, thereby increasing the device's ability to resist stiction.

Figure 5 shows an illustrative MEMS device plane of an out-of-plane sensing accelerometer, according to some embodiments of the present disclosure. Those of ordinary skill in the art will appreciate that fig. 5 may be modified in various ways in accordance with the present disclosure. In an exemplary embodiment, the out-of-plane sensing accelerometer includes a first sensor portion 580, a second sensor portion 585 and a MEMS stationary portion 590.

In some embodiments, the first sensor portion 580 may include the anchor region 510. The example anchor region 510 may include a plurality of anchor portions, each anchor portion anchored to each of the cap layer and the substrate layer and fixed within the MEMS device layer. The axis of symmetry 560 and the axis of rotation 564 may intersect at a center point of the anchor region 510, where the axis of symmetry 560 extends along the y-axis and the axis of rotation 564 extends perpendicular to the axis of symmetry 560 along the x-axis.

In some embodiments, paddle mass 512 may be coupled to the left portion of the anchor area by torsion bar 503 and paddle mass 514 may be coupled to the right portion of the anchor area by torsion bar 505. Torsion bars 503 and 505 may have appropriate aspect ratios to support the movable components of first sensor portion 580 (e.g., paddle mass 512, paddle mass 514, and proof mass 502), while springs 501 and 507 couple proof mass 502 in a manner that allows out-of-plane rotation of proof mass 502 about axis of rotation 564 in response to out-of-plane motion of sensor portion 580.

The paddle masses 512 and 514 may be coupled to the asymmetric proof mass portion 504 of the proof mass 502 by respective springs 501 and 507. Each spring 501 and 507 may be substantially rigid along the x-axis, may allow limited movement along the x-axis, and may have significant torsional compliance to allow rotational movement of the proof mass 502 relative to the paddle masses 512 and 514. Collectively, springs 501 and 507 may be aligned with torsion bars 503 and 505 along the x-axis to form an axis of rotation 564 for first sensor portion 580. One or more sense electrodes (not depicted) may be located on the substrate below the proof mass 502 to form one or more sense capacitors. In an exemplary embodiment, paddle electrodes may be associated with each of the paddle masses 512 and 514 such that offset compensation (e.g., due to temperature effects, shear forces, manufacturing, or packaging) may be performed based on the relative out-of-plane position of the paddle masses 512 and 514.

The proof mass 502 may include a symmetric proof mass portion 504 and an asymmetric proof mass portion 506 extending from the symmetric portion 504 in a direction parallel to the axis of rotation. The symmetric proof mass portion 504 may be symmetric about an axis of symmetry 560. Since the asymmetric proof mass portion 506 extends from the symmetric proof mass portion 506, forces such as impacts can cause rotational motion, rather than translational motion, of the proof mass 502 about the anchor region 510, and the angle of the rotational motion due to the impact can be increased as compared to a symmetric proof mass.

In some embodiments, the MEMS stationary portion 590 may include a plurality of buffer stops positioned adjacent the proof mass 502. In an exemplary embodiment, each of the buffer stops positioned adjacent to the proof mass 502 may have a generally rectangular shape and may be positioned to limit translational motion in a particular direction and inhibit rotation beyond a rotation threshold in the range of 5-35 degrees (e.g., 15 degrees in an exemplary embodiment); although suitable buffer stops may be positioned at different locations on the MEMS fixed portion 590, the buffer stops may have different shapes, and in some embodiments, buffer stops may be added or removed. In one embodiment, a buffer stop 534 may be positioned on the lower left side of the proof-mass section 504 to limit rotation and negative y-axis motion, buffer stops 550 and 552 may be positioned on the upper left side of the proof-mass section 504 to limit rotation and negative x-axis motion, a buffer stop 548 may be positioned on the upper left side of the proof-mass section 504 to limit rotation and positive y-axis motion, a buffer stop 542 may be positioned on the upper right side of the asymmetric proof-mass section 506 to limit rotation and positive y-axis motion, and a buffer stop 540 may be positioned on the upper right side of the asymmetric proof-mass section 506 to limit rotation and positive x-axis motion.

In some embodiments, the second sensor portion 585 can include an anchor region 530. The example anchor region 530 may include a plurality of anchor portions, each anchor portion anchored to each of the cap layer and the substrate layer and fixed within the MEMS device layer. Symmetry axis 562 and rotation axis 564 may intersect at a center point of anchor region 530, where symmetry axis 562 extends along the y-axis and rotation axis 564 extends perpendicular to symmetry axis 560 along the x-axis. In the exemplary embodiment of fig. 5, the second sensor portion 585 may have the same axis of rotation as the first sensor portion 580, although in other embodiments their axes of rotation may be parallel or at an angle to each other.

In some embodiments, paddle mass 532 may be coupled to a left portion of anchor region 530 by torsion bar 513 and paddle mass 534 may be coupled to a right portion of anchor region 530 by torsion bar 515. The torsion bars 513 and 515 may have suitable aspect ratios to support the movable components of the second sensor portion 580 (e.g., the paddle mass 532, the paddle mass 534, and the proof mass 522) while allowing out-of-plane rotation of the proof mass 522 about the rotation axis 564 in response to out-of-plane motion of the proof mass 522.

The paddle masses 532 and 534 can be coupled to the asymmetric proof mass portion 524 of the proof mass 522 by respective springs 511 and 517. Each of the springs 511 and 517 may be substantially rigid along the x-axis, may permit limited motion along the y-axis, and may have significant torsional compliance to enable rotational motion of the proof mass 522 about the axis of rotation 564. The springs 511 and 517 together may be aligned with the torsion bars 513 and 515 along the x-axis to form an axis of rotation 564 of the second sensor portion 585. One or more sense electrodes (not depicted) may be positioned on the substrate below the proof mass 522 to form one or more sense capacitors. In an exemplary embodiment, additional paddle electrodes may be associated with each of the paddle masses 532 and 534 such that offset compensation (e.g., due to temperature effects, shear forces, manufacturing, or packaging) may be performed based on the relative out-of-plane positions of the paddle masses 532 and 534.

The proof mass 522 may include a symmetric proof mass portion 524 and an asymmetric proof mass portion 526 extending from the symmetric portion 524 in a direction parallel to the axis of rotation. The symmetric proof mass section 524 may be symmetric about an axis of symmetry 562. Since the asymmetric proof mass section 526 extends from the symmetric proof mass section 526, forces such as impacts may cause rotational motion of the proof mass 522 about the anchor region 530 rather than translational motion, and the angle of the rotational motion due to the impact may be increased as compared to a symmetric proof mass.

In some embodiments, the MEMS stationary portion 590 may include a plurality of buffer stops positioned adjacent the proof mass 522. In an exemplary embodiment, each of the buffer stops positioned adjacent the proof mass 522 may have a generally rectangular shape and may be positioned to limit translational motion in a particular direction and inhibit rotation beyond a rotation threshold in the range of 5-35 degrees (e.g., 15 degrees in an exemplary embodiment); although suitable buffer stops may be positioned at different locations on the MEMS fixed portion 590, the buffer stops may have different shapes, and the buffer stops may be added or removed in some embodiments. In one embodiment, the buffer stop 574 may be positioned on the upper right side of the proof mass section 524 to limit rotation and positive y-axis motion, the buffer stops 570 and 572 may be positioned on the lower right side of the proof mass section 524 to limit rotation and positive x-axis motion, the buffer stop 568 may be positioned on the lower right side of the proof mass section 524 to limit rotation and negative y-axis motion, the buffer stop 562 may be positioned on the lower left side of the asymmetric proof mass section 526 to limit rotation and negative y-axis motion, and the buffer stop 560 may be positioned on the lower left side of the asymmetric proof mass section 526 to limit rotation and negative x-axis motion.

Linear acceleration in the positive z-direction can cause the proof mass 502 to rotate in a counterclockwise direction about the rotation axis 564, such that the positive y-axis portion of the proof mass 502 (e.g., including the larger portion of the symmetric proof mass 504 and all of the asymmetric proof mass portion 506) rotates out-of-plane in the negative z-direction, while the negative x-axis portion of the proof mass 502 (e.g., the small portion of the symmetric proof mass portion 504) rotates out-of-plane in the positive z-direction. The positive Z direction. Sensing electrodes may be positioned under portions of the proof mass 502 to sense the change in capacitance due to this motion. Linear acceleration in the positive z-direction may cause the proof mass 522 to rotate in a clockwise direction about the rotation axis 564, such that a negative y-axis portion of the proof mass 522 (e.g., including a larger portion of the symmetric proof mass 524 and all of the asymmetric proof mass portion 526) rotates out-of-plane in the negative z-direction, while a positive y-axis portion of the proof mass 522 (e.g., a small portion of the symmetric proof mass portion 524) rotates out-of-plane in the positive x-direction. Sensing electrodes may be located under portions of the proof mass 522 to sense changes in capacitance due to this motion.

Linear acceleration in the negative z-direction can cause the proof mass 502 to rotate in a clockwise direction about the rotation axis 564, such that the positive y-axis portion of the proof mass 502 (e.g., including the larger portion of the symmetric proof mass 504 and all of the asymmetric proof mass portion 506) rotates out-of-plane in the positive z-direction, while the negative x-axis portion of the proof mass 502 (e.g., the small portion of the symmetric proof mass portion 504) rotates out-of-plane in the negative z-direction. Sensing electrodes may be positioned under portions of the proof mass 502 to sense the change in capacitance due to this motion. Linear acceleration in the negative z-direction may cause the proof mass 522 to rotate in a clockwise direction about the rotation axis 564, such that a negative y-axis portion of the proof mass 522 (e.g., including a larger portion of the symmetric proof mass 524 and all of the asymmetric proof mass portion 526) rotates out-of-plane in the positive z-direction, while a positive y-axis portion of the proof mass 522 (e.g., a small portion of the symmetric proof mass portion 524) rotates out-of-plane in the negative z-direction. Sensing electrodes may be positioned under portions of the proof mass 522 to sense changes in capacitance due to this motion.

Referring to fig. 5, the MEMS movable components of the first and second sensor portions 580, 585 may be positioned proximate to the other movable components and the MEMS fixed portion 590 located in the plane of the MEMS device. Asymmetric proof mass portions 506 and 526 may create a lever effect with respect to applied shock or vibration forces, which may reduce stiction in the proof mass and other MEMS components.

The foregoing description contains exemplary embodiments in accordance with the disclosure. These examples are provided for purposes of illustration only and not for purposes of limitation. It is to be understood that the present disclosure may be embodied in forms other than those explicitly described and illustrated herein, and that various modifications, optimizations, and variations consistent with the claims below may be practiced by those of ordinary skill in the art.